1. Technical Field
The present disclosure relates to a method for making carbon nanotube film.
2. Description of Related Art
Carbon nanotubes are hollow tubular structures having excellent mechanical, thermal, and electrical properties. Their unique properties make carbon nanotubes ideal candidates for potential applications in different fields. However, the carbon nanotubes with nanoscale dimension are difficult to process. Attempts to fabricate carbon nanotube structure with macroscale dimension for easy processing include fabricating the carbon nanotube structure into wire shapes, film shapes, or other macroscopic shapes.
Recently, a carbon nanotube film has been fabricated by drawing from a carbon nanotube array disclosed by patent application US20080248235A to Feng et al. The carbon nanotube film is a free-standing structure and includes a plurality of carbon nanotubes joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes in the carbon nanotube film are substantially aligned along the same direction. Thus, this carbon nanotube film has good thermal and electrical conductivity properties along the direction of the aligned carbon nanotubes. Therefore, the carbon nanotube film can be used in many different fields.
However, the size of the carbon nanotube film directly drawn from the carbon nanotube array is restricted by the size of the carbon nanotube array. During the growth of the carbon nanotube array using a CVD method, the inner gas pressure of the tube furnace is less than the atmospheric pressure outside the tube furnace. Therefore, the sidewall of the tube furnace must bear an inward pressure difference applied thereon. If the tube furnace with a diameter of about 10 inches and a length of about 2 meters has the inner gas pressure of about 10 torrs, the pressure difference between the inside and the outside of the tube furnace is about 50,000 Newton. However, if the diameter of the tube furnace is increased to 40 inches, the pressure difference could reach to about 200,000 Newton. Further, as the diameter of the tube furnace increases, the curvature of the sidewall of the tube furnace decreases, thus weakening the support of the sidewall and may cause damage to the tube furnace.
Accordingly, the tube furnace with a larger diameter cannot be achieved. The conventional tube furnace for growing the carbon nanotube array has a diameter of about 10 inches. Therefore, a substrate disposed inside the tube furnace should have a diameter less than 10 inches, such as 8 inches. An original carbon nanotube film directly drawn from the carbon nanotube array grown on that 8-inch substrate has a width restricted to 8 inches. The area and the width of the carbon nanotube film are also restricted.
What is needed, therefore, is to provide a method for making a carbon nanotube film having a relatively large size.